Shutters are used in infrared imagers for periodic correction of spatial noise in video images caused by temporal changes in image acquisition module parameters on the pixel scale. The shutters are engaged periodically (e.g. once per minute). Infrared imagers commonly employ mechanical flag or iris shutters. Operation of such shutters is slow. It may take several video frames for shutters to engage and disengage. Typically, they block the scene for the duration of the order of hundreds of milliseconds, which causes noticeable breaks in the video stream. Also, they are noisy, consume considerable power, and their assemblies are relatively large and heavy.
In thermal imagers, a fast shutter that blocks the video for only one or two frames would create “shutterless” experience for the user, i.e. the video stream will not be noticeably interrupted. However, the time required for imager pixels to reach thermal equilibrium imposes a limit on how fast the shutter operation can be performed. It may not allow use of the full speed of the shutter. The thermal time constants of uncooled imager pixels may be comparable to or longer than the duration of one or two frames, therefore this interval will be insufficient for the imager to thermalize to the thermally uniform scene presented by the shutter. This would result in residual spatial noise left in the image stream after engagement of the fast shutter.
What is needed, therefore, are imagers with improved performance to meet increasing system requirements.